Field of the Invention
Yarn breakage detecting systems disclosed in Japanese Laid-Open Patent (Kokai) Application Nos. 50-25860, 51-35759 and 50-25861 (cited references 1, 2 and 3, respectively) detect the number of warp yarns forming a warp and determine that yarn breakage has occurred when the number of the warp yarns is smaller than a predetermined number. The yarn breakage detecting systems disclosed in the cited references 1 and 2 employ a fixed yarn detector which is held fixedly, and the yarn breakage detecting system disclosed in the cited reference 3 employs a moving yarn detector which moves along the warp.
The disadvantages of these prior art yarn breakage detecting systems are exposed when the prior art yarn breakage detecting systems are applied to detecting the breakage of warp yarns of a wide warp. First, the fixed yarn detector is incapable of accurately detecting the warp yarns in the opposite ends of the warp remote from the yarn detector and hence the yarn breakage detecting system is unable to count the number of warp yarns accurately, because the virtual pitches of the warp yarns remote from the fixed yarn detector as viewed from the fixed yarn detector are small and the fixed yarn detector is unable to distinguish individual warp yarns separately.
The moving yarn detector requires a relatively long time to scan all the warp yarns and hence the yarn breakage detecting system is unable to detect the breakage of a warp yarn as soon as it is broken. Consequently, it is possible for serious problems to occur, such as the additional breakage of warp yarns caused by the broken warp yarn and the winding of the broken warp yarn on the cloth beam. The yarn breakage detecting system employing the fixed yarn detector has similar disadvantages.
Such disadvantages may be overcome by dividing the width of the warp into a plurality of monitoring ranges and allocating a plurality of yarn detectors respectively to the plurality of monitoring ranges. Such a means, however, entails other problems; that is, since the warp yarns swing to make the boundaries of the monitoring ranges indistinct and the yarn detectors vibrate and are unable to detect the numbers of the warp yarns in the corresponding monitoring ranges accurately, it is impossible to count the number of the warp yarns accurately. Accordingly, it is impossible to apply such a means to practical use.